Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det
High-Efficiency Broadband Mid-Infrared Absorption in Asymmetrically Matched Metallic Meanders: Development of Ti40V60 Alloy based LEKIDs for Mid-Far IR
Shilpam Sharma, Shekhar Chandra Pandey, Anudeep Singh et al. (+3 more)
Fast, highly sensitive, and broadband detectors operating in the mid-to-far-infrared (MIR-FIR) spectral region are essential for applications ranging from astrophysics to time-resolved spectroscopy using laboratory-based sources and beamlines at Infrared Free-Electron
Laser (IR-FEL) facilities. Conventional Lumped Element Kinetic Inductance Detectors (LEKID) achieve high optical efficiency using resonant quarter wavelength ({\lambda}/4) backshort cavities. However, this cavity-based approach is inherently narrowband and becomes optomechanically challenging at the mid to far infrared (MIR-FIR) wavelengths. Here, we present a completely backshort-free LEKID absorber architecture that achieves broadband absorption exceeding 50%. The meander absorbers were fabricated from a superconducting Ti-V
alloy and characterized using IR radiation from the IR-FEL at RRCAT, India. By illuminating through the silicon substrate and matching the meander's sheet resistance to the silicon substrate's wave impedance, the front-side reflection is strongly suppressed. Simultaneously, the sub-wavelength periodicity of the dense meander inhibits propagating transmission into free space via evanescent wave confinement. This combined mechanism drives efficient Ohmic dissipation within the metallic meander, yielding an experimental absorption efficiency ranging from 50% to 90% across the 12.5-30 micrometer wavelength range. The cavity-free design greatly simplifies the fabrication of the focal plane array while providing the broadband response required for next-generation detectors. To assess the suitability of the Ti40V60
alloy as an active superconducting detector material, a test LEKID resonator was also designed, fabricated, and experimentally characterized.
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All authors Shilpam Sharma, Shekhar Chandra Pandey, Anudeep Singh, Shankar Lal, R. S. Saini, M. K. Chattopadhyay
Earth and Planetary Astrophysics · Cross-listed from physics.geo-ph
Satellite gravity constraints on inner core viscosity and LLVPs density anomalies
Yachong An, Hao Ding, Fred D. Richards et al. (+3 more)
Constraining the physical properties of Earth's deep interior, particularly the viscosity of the solid inner core and the density structure of large low-velocity provinces (LLVPs), remains a major challenge in geophysics. Here we develop a unified dynamical framework that combines mantle-inner core gravitational coupling (MICG) with torsional oscillations in the fluid outer core and show that their interaction can produce a distinct and testable geodetic signature. Guided by this prediction, we analyze satellite
gravity observations together with independent corrections for surface mass variability. We identify a robust approximately 6-year signal in the Stokes coefficient Delta S22, while no corresponding stationary signal is detected in Delta C22. A signal with the same periodicity is independently detected in length-of-day variations (Delta LOD), and the two signals exhibit a near anti-phase relationship. Interpreting this coupled signature within the proposed framework allows us to constrain the inner core viscosity to approximately 4.6 (+/- 1.8) x 10^16 Pa s and the equatorial relief of the inner core boundary to a semi-axis difference of about 200 +/- 70 m. The inversion further indicates mean density anomalies of +5.5 (+/- 0.6) per mil at the base of LLVPs. These results indicate that satellite gravimetry provides a direct observational window into deep-Earth dynamics and the physical properties of Earth's deep interior.
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All authors Yachong An, Hao Ding, Fred D. Richards, Weiping Jiang, Jiancheng Li, Wenbin Shen
Astrophysics of Galaxies
Disentangling chemical evolution histories with phylogenetic trees
Rebeca Canales, Paula Jofré, Claudia Aguilera-Gómez et al. (+6 more)
Chemical abundances encode the fossil record of
galaxy evolution in a complex and diverse way that requires innovative approaches to reconstruct
galactic histories. We investigate the power of using phylogenetic methods to disentangle different evolutionary pathways in analytical chemical
evolution models. We ran 1024 one-zone chemical
evolution models using flexCE. The resulting chemical abundances are combined with those of two fiducial models, mw-fid and dw-fid, and then used both to determine which combinations produce two-branched phylogenetic trees, as well as how purely these trees split the two input models. We used random forests and Shapley analysis to predict which model combinations return well-separated trees and explain which input parameters are most important for this. We also studied the abundance patterns, as well as
star formation rates, mass accumulation, and branch lengths. We found that {\eta}, the mass-loading
outflow parameter in flexCE, had the largest impact in separating models into separate branches, due to its importance in driving the chemical enrichment rates and total abundances.
Star formation rates and mass accumulation had some impact on {\eta}, but no direct relation between these quantities and the abundances was found. We also found that branches connected through the most metal rich tips in our trees, which is opposite to how phylogenetic trees connect in biological systems. Phylogenetic trees help to reconstruct histories when there is information that is inherited between generations, which is the case of the chemical elements in
galaxy evolution. Branch
topologies can provide information about the rates of evolutionary change of the various populations, and the connection between branches also contains information about their shared history. This work brings us a step further understanding
galaxy evolution through cross-disciplinary research.
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All authors Rebeca Canales, Paula Jofré, Claudia Aguilera-Gómez, Payel Das, Robert Yates, Theosamuele Signor, Patricia Tissera, Xia Hua, Robert Foley
Solar and Stellar Astrophysics
A consistency check for the calibration of 5303Å solar coronal emission line observations with Aditya-L1/VELC
V. Muthu Priyal, R. Ramesh, Jagdev Singh et al. (+2 more)
We carried out radiometric calibration of the Visible Emission Line Coronagraph (VELC) onboard Aditya-L1 at 5303Å using observations of the Sun itself, a novel approach compared to the calibration using bright
stars in the other currently operational space
solar coronagraphs. The measured VELC detector count corresponding to the center of Sun's disk is ${\approx}(1.70{\pm}0.12){\times}10^{8}\, \rm sec^{-1}{\AA}^{-1}$, which relates to Sun's flux at 1\,AU in 5303Å, ${\approx}3.0456{\times}10^{6}\, \rm {erg\,sec^{-1} cm^{-2} {\AA}^{-1}}$. We verified the above calibration using observations of the bright
star Sirius-A whose estimated flux at 1\,AU in 5303Å is ${\approx}1.44{\times}10^{-8}\,\mathrm{erg\,sec^{-1} cm^{-2} \AA^{-1}}$. The expected detector count with VELC in this case is ${\approx}19{\pm}1.4\, \rm sec^{-1}{\AA}^{-1}$, and the measured count is ${\approx}23{\pm}0.4\, \rm sec^{-1}{\AA}^{-1}$. The reasonable agreement between the expected and observed values for Sirius-A in this initial consistency check after two years of observations with VELC, indicates that measurements of coronal brightness at 5303Å with the VELC and its conversion into absolute physical units using observations of the Sun disk light are in order. Using the Sirius-A observations we measured the point spread function (PSF) of the VELC in its 5303Å channel also. Its full width at half maximum (FWHM) is ${\approx}3.8^{\prime\prime}$.
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All authors V. Muthu Priyal, R. Ramesh, Jagdev Singh, K. Sasikumar Raja, P. Savarimuthu
High Energy Astrophysical Phenomena
Bayesian analysis of the shear modulus in the neutron-star crust
T. Diverrès, G. Montefusco, A. F. Fantina et al. (+1 more)
The elastic properties of the
neutron-
star crust are important for the calculations of crustal modes. In particular, the ability of the crust to support shear stresses has been connected to observations of quasi-periodic oscillations and to crust deformations potentially emitting gravitational waves. In this work, we assess the uncertainties in the shear modulus and shear speed in the
neutron-
star outer and inner crust. To this aim, we performed a
Bayesian analysis of the shear properties of the
neutron-
star crust at zero temperature starting from both a non-informative and a
nuclear-physics-informed prior. For the treatment of inhomogeneous matter in the crust, we relied on the one-component
plasma approximation, with a (semi-)classical treatment of the ions. We show that the use of a
nuclear-physics-informed prior has a non-negligible impact on the prediction of the elastic properties of the crust. The frequency of the fundamental torsional crustal modes we obtain is compatible with the low-frequency range of observed quasi-periodic oscillations, our estimates lying in the interval $\approx 20 - 50$~Hz. Although the different considered priors lead to compatible results, the inclusion of
nuclear-physics experimental information in the prior considerably reduces the uncertainties in the prediction of the elastic properties of the crust, potentially constraining the predicted frequency of the crustal modes.
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All authors T. Diverrès, G. Montefusco, A. F. Fantina, F. Gulminelli
Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
Detectability to extreme mass ratio inspirals with alternative space-based detector networks
Chao Zhang and Gang Wang
Extreme mass ratio inspirals (EMRIs) are among the primary targets for space-based gravitational-wave (GW) detectors, providing valuable opportunities to study
stellar-mass compact objects orbiting supermassive black holes (SMBHs) and to probe
gravity in the strong-field regime. As the LISA, TAIJI, and TianQin missions are expected to operate around 2035, joint observations by multiple detectors may provide enhanced measurement capabilities compared to individual missions. In this work, we investigate the detectability and parameter-constraint prospects for EMRIs using global detector networks composed of LISA, TianQin, and two alternative TAIJI orbital configurations. Employing Fisher information
matrix analysis, we find that joint observations improve source localization relative to a standalone LISA mission, with sky-localization uncertainties reduced by up to two orders of magnitude for a one-month observation period. We further find that a three-detector network (LISA-TAIJI-TianQin) operating for one month yields parameter constraints comparable to, and in some cases tighter than, those obtained from a one-year observation by LISA alone. This result indicates that network observations can partially compensate for shorter observation durations in parameter inference. Furthermore, we evaluate measurement uncertainties in concurrent dual-signal scenarios: (i) two EMRIs orbiting the same SMBH and (ii) two EMRIs with identical intrinsic parameters but different sky locations and orientations. The results indicate that differences in the detector responses associated with the source geometries reduce correlations between overlapping signals, allowing the sources to remain distinguishable even for a standalone mission. The inclusion of multiple detector constellations further improves source localization and tightens parameter constraints in these concurrent-source scenarios.
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High Energy Astrophysical Phenomena
GRB 250706B/C: Insight-HXMT Discovery of a High-Luminosity Burst as a Candidate for Fallback-Regulated Accretion in the Prompt Emission
Chen-Wei Wang, R. Moradi, Shao-Lin Xiong et al. (+15 more)
Fallback
accretion in collapsar models is often associated with underluminous gamma-ray bursts (GRBs), leading to the widespread view that fallback-fed engines may be intrinsically inefficient at producing high-luminosity events. In this Letter, we present GRB 250706B/C, a luminous long GRB observed by Insight-HXMT that exhibits an unusual combination of extreme short-timescale variability and coherent large-scale temporal
evolution. The
prompt emission contains at least 79 resolved pulses and a minimum variability timescale of $\sim11$ ms. The pulse widths are nearly independent of
photon energy and span a broad distribution with a median FWHM of $\sim0.30$ s, while the waiting times between adjacent pulses have a median of $\sim0.38$ s. The
prompt-emission envelope exhibits a prolonged rise described by $F(t)\propto (t-t_0)^{0.47\pm0.01}$ followed by a rapid decline. Despite substantial pulse-to-pulse fluctuations, neither the pulse widths nor the waiting times show significant secular
evolution during the main emission episode. These features indicate the coexistence of two distinct temporal components, including a slow evolving rising luminosity envelope and rapid
stochastic variability. Such behavior is consistent with scenarios in which a time-dependent engine-feeding history regulates the large-scale emission while internal dissipation within the relativistic
outflow produces the pulse structure. Within this context, GRB~250706B/C may represent a fallback-fed collapsar operating on a high-luminosity branch, suggesting that fallback itself does not necessarily limit the luminosity scale of GRBs.
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All authors Chen-Wei Wang, R. Moradi, Shao-Lin Xiong, Shuang-Nan Zhang, Zheng-Hang Yu, Wen-Jun Tan, Hao-Xuan Guo, Xiao-Bo Li, Cheng-Kui Li, Jia-Cong Liu, Xing-Hao Luo, Yang-Zhao Ren, Yue Wang, Sheng-Lun Xie, Wang-Chen Xue, Yuan-Zao Xue, Peng Zhang, Chao Zheng
Solar and Stellar Astrophysics
Predictability of a solar flare in May 2024 using observational data-driven MHD simulations
Takafumi Kaneko
We examined the applicability of observational data-driven magnetohydrodynamic (MHD) simulations to
flare prediction. The target event was the X1.6
flare that occurred in NOAA AR 13663 at 02:22 UT on 3 May 2024. We employed a velocity-driven model, in which the photospheric velocity field was derived from the time-series magnetograms to use as the boundary input. The simulation showed a rapid increase in both thermal and kinetic energy density around the actual onset time and location of the X1.6
flare. We revealed that the
flare was triggered by two-step reconnection, in which the initial tether-cutting reconnection facilitated the subsequent breakout reconnection. We further examined whether the
flare could be reproduced when the boundary input was stopped prior to the actual
flare onset time, assuming the situation in which the
flare must be predicted using the data before it actually occurs. When the photospheric
magnetic field was fixed more than 1 hour before the actual
flare onset time, the
flare was not reproduced in the simulations. In contrast, when the photospheric velocity field at the final observation time was incorporated to infer the subsequent
magnetic evolution, the prediction lead time could be extended beyond 1 hour. On the other hand, quantitative prediction of the magnitude of
flares remains a subject for future study.
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Instrumentation and Methods for Astrophysics · Cross-listed from cs.CV
Semi-supervised Source Detection in Astronomical Images: New Benchmark and Strong Baseline
Longhan Feng, Zihuang Cao, Ali Luo et al. (+5 more)
Source detection in modern observational astronomy is a cornerstone for localizing and identifying
stellar sources accurately. It is crucial for studies such as
stellar population synthesis and cosmological parameter estimation. However, the characteristics of astronomical images, including high density, the effect of point spread functions and low signal-to-noise ratios, significantly challenge the latest advanced object detectors. Besides, fully-supervised detection methods are hardly practical, due to the significant difficulty in annotating dense, small, and faint sources in astronomical images. To tackle the scarcity of astronomical
datasets, we introduce a new comprehensive
benchmark (LAMOST-DET), comprising 18,400 astronomical images and 728,898 source instances. Upon the
dataset, we further devise a novel semi-supervised learning framework coined Nova Teacher, capable of detecting dense sources effectively given sparse annotations. It integrates source light enhancement module, confidence-guided pseudo-supervision, and cross-view complementary mining in a dual-teacher paradigm. Extensive experiments on LAMOST-DET show that, Nova Teacher consistently improves previous competitors by 4.04% and 5.22% mAP under two semi-supervised settings. Additionally, our method competes against other detectors on a natural image
dataset, validating its generalization ability to various scenarios. The source code is available at https://github.com/AcWiz/NovaTeacher.
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All authors Longhan Feng, Zihuang Cao, Ali Luo, Yuanhao Guo, Shuilian Yao, Yixin Guo, Qi Jia, Yu Liu
Cosmology and Nongalactic Astrophysics
Optimising ultra-light dark matter searches with ground-based interferometers
Paola C. M. Delgado, Ornella J. Piccinni and Federico R. Urban
Ultra-light dark matter fields induce nearly monochromatic signals in gravitational-wave detectors through their coupling to the Standard Model. Their spectral morphology exhibits features caused by sidereal modulation that, for frequencies below $\sim 30~$Hz, enable discrimination between
spin-1 and
spin-2 ultra-light dark matter signals, provided sufficient signal-to-noise ratio. In the context of LIGO–Virgo–KAGRA search techniques, we show that incorporating these spectral features can improve current excess-power constraints at low frequencies by up to $\sim36\%$. Additionally, we propose an optimised implementation of the cross-correlation statistics within the Band-Sampled-Data framework, enhancing the sensitivity of cross-correlation searches across nearly the entire frequency range, reaching up to $\sim42\%$ at low frequencies and $\sim35\%$ at high frequencies.
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Solar and Stellar Astrophysics
Ages and ZAMS spin distribution of stars in detached eclipsing binaries
T. Merle, W. Van Rensbergen, L. Siess et al. (+4 more)
Benchmarking fundamental
stellar properties is essential for calibrating evolutionary models and establishing empirical relationships between mass, radius, luminosity and related
stellar properties. We determine the current ages and initial equatorial velocities at the Zero-Age Main Sequence (ZAMS) for a well-characterized sample of 108 detached main-sequence eclipsing binaries. Evolutionary tracks from the ZAMS to the present are calculated by accounting for
tidal interactions, including meridional circulation, and angular momentum loss via
stellar winds, under the assumption of circular orbits. System ages are derived by identifying the evolutionary stage at which the calculated radii of both
stellar components best match the observed values. While initial velocities for currently synchronized systems cannot be uniquely constrained, as a wide range of initial states naturally converges to synchronisation over time, we are able to determine unique solutions for ZAMS
spin velocities in systems that remain asynchronous today. Our models successfully reproduce observed present-day equatorial velocities with a precision of 1%. Two systems, HD~71636 and V396~Cas, were found to have primaries with initially retrograde
spin at ZAMS. We also find an increasing dispersion of
spin velocities with age. Our results demonstrate that
tidal and evolutionary effects in binary systems actively counteract rotational deceleration from
stellar winds, effectively preventing the substantial
spin-down that typically characterizes the
evolution of isolated single
stars.
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All authors T. Merle, W. Van Rensbergen, L. Siess, J.P. De Greve, K. Jansen, S. Van Eck, G. Van de Steene
Instrumentation and Methods for Astrophysics
On the Nonlinear Dependence of Underground Muon Rate on Atmospheric Temperature Observed at Daya Bay
Lei Liao, Taichong Ge and Zhe Wang
The underground
cosmic-ray
muon rate is modulated by atmospheric temperature. It can be explained by the theories of Barrett, Gaisser, and others. However, the Daya Bay
Neutrino Experiment observes a nonlinear temperature dependence. We find that, when deriving the temperature dependence of the
muon rate, existing theories consider only the impact of the local temperature on
muon production at the layer where
muons are produced. In this work, we provide a more general solution to the cascade equations that fully depicts how the entire temperature profile influences the final
muon rate. The corresponding definitions of the effective temperature weight and temperature coefficient are also presented. We have examined the results using the numerical tool MCEq with real atmospheric temperature inputs. A linear modulation is recovered and verified. This work can help explain the nonlinear effect observed at Daya Bay and provide a more refined theoretical framework for calculating the temperature coefficient in other experiments.
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Earth and Planetary Astrophysics
CORALIE radial-velocity search for companions around evolved stars (CASCADES) V. Three planetary companions and achievable precision
P. Figueira, E. Fontanet, J. P. Faria et al. (+9 more)
Aims. We expand the planetary census around massive
stellar hosts through a long-term campaign of high-precision radial velocity (RV) measurements on evolved
stars. Methods. We analyse data acquired with the CORALIE spectrograph covering 15-18 years on HD125136, HD127195, and HD220218.
Stellar parameters are derived through different methods for a comprehensive characterization of each
star. We then evaluate the presence of planetary signals in the RV time series using the
Bayesian inference tool kima. Finally, we design an observing strategy aimed at mitigating the impact of pulsations on evolved
stars and test its effectiveness on the low-luminosity red
giant HD127195. Results. We detect signals that are accurately modelled by Keplerian curves in the RV data of the three
stars: one on HD 125136, two on HD 127195, and one on HD 220218. While the signals on the first two
stars seem to be of planetary origin, the signal on the third one shows several signs of
stellar activity. We therefore identify a planetary companion around HD125136 with a minimum mass of 2.26 MJup on an 850 d orbit, and on HD127195 we identify a system composed of
planets with 0.66 MJup and 0.78 MJup with orbital periods of 535 d and 834 d, respectively. Conclusions. We detect three massive
planets around two low-luminosity red
giant stars in a region of the parameter space that is poorly populated in both
stellar mass and planetary orbital periods. The dedicated observing campaign on HD127195 showcases how
stellar pulsations can be efficiently averaged out to below 5 m/s in low-luminosity
giant stars.
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All authors P. Figueira, E. Fontanet, J. P. Faria, M. Esseldeurs, E. Friden, A. Leleu, R. Luque, G. Ottoni, D. Ségransan, M. Stalport, S. Tavella, S. Udry
Instrumentation and Methods for Astrophysics
Statistical Estimation and Correction of Model-Measurement Bias in Time-Dependent Correction Factors of KAGRA
Shingo Hido, Takahiro Yamamoto, Dan Chen et al. (+2 more)
Calibration of gravitational-wave detectors reconstructs the strain h(t) from the detector output, and bias and uncertainty in this reconstruction directly affect downstream analyses. In ground-based interferometers, time-dependent correction factors (TDCFs) are estimated from calibration lines to track temporal variations of the detector response, while the underlying model parameters are periodically updated using broadband swept-sine calibration measurements (SSCMs). However, if a model-measurement bias exists between the measured transfer function and the reference model, the TDCFs inferred from calibration lines can introduce a systematic deviation into the reconstructed strain. We propose a statistical framework to estimate and correct this bias using repeated measurement-to-model ratios at the calibration-line frequencies. The bias correction factors are estimated with a rolling random-effects model based on restricted maximum likelihood (REML) and incorporated into the TDCF estimation, with their uncertainty propagated to the reconstructed response. Applying the method to KAGRA O4c data, we find that the uncorrected response shows deviations of up to approximately 7% in magnitude and 5 degrees in phase relative to the SSCM-based reference in representative examples. The correction reduces these deviations, with a modest increase in the propagated uncertainty due to the included correction-factor uncertainty. This framework provides a practical way to combine broadband reference models with calibration-line-based tracking when model-measurement bias is present.
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All authors Shingo Hido, Takahiro Yamamoto, Dan Chen, Takahiro Sawada, Shinji Miyoki
Earth and Planetary Astrophysics
Parameter Effects in Circumplanetary Disk Spectra and Prospects for Spectral Fitting
Xilei Sun, Gabriel-Dominique Marleau and Shang-Fei Liu
With the commissioning of the James Webb Space
Telescope (JWST), near- and mid-infrared observations are rapidly extending into the wavelength regime where emission from small
dust grains in circumplanetary disks (CPDs) is expected to dominate. We aim to systematically investigate how individual physical parameters of CPDs shape their infrared spectra and to improve the robustness of spectral fitting and physical interpretation of current and future observations. Building on our previous parametric CPD models, we employ a parameter-grid approach combined with radiative transfer simulations to explore the dependence of observable spectra on disk structure and
dust properties. We identify the physical mechanisms responsible for the main spectral features and parameter degeneracies, and present the global trends emerging from the parameter study. We also demonstrate the applicability of the models by fitting representative observational data. Our results provide a structured theoretical framework for interpreting near- and mid-infrared observations of CPDs with JWST and related facilities.
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Astrophysics of Galaxies
The origin of WHAM Point Source~46
S. R. Kulkarni, Zeren Lin, Charles Beichman et al. (+7 more)
The Wisconsin H$\alpha$ Mapper (WHAM) surveyed the entire
Galactic sky in H$\alpha$ ($\vert v_{\rm LSR}\vert \lesssim 100\, {\rm km\,s^{-1}}$) to approximately 0.1\,Rayleigh (R), albeit with a 1-degree beam. %The resulting WHAM Sky Survey, along with large area %imaging in [\ion{S}{2}] and [\ion{N}{2}], laid the foundation for Warm Ionized %Medium (WIM) science. \cite{rcm+05} reported “point sources" which stood out against the
Galactic background in space and velocity. Half of the sources are associated with plausible planetary nebulae and OB
stars. Reynolds et al (2005) suggested sub
dwarfs for one quarter of the sources. Here, we investigate one such source, WPS\,46, for which Reynolds et al (2005) suggested the sub-
dwarf PG\,0931+691 to provide the source of ionization. With the Keck
Cosmic Web Imager we found numerous nebular emission lines within the vicinity of WPS\,46, but we failed to find H$\alpha$ emission in the arc-minute vicinity of PG\,0931+691. The line ratios (BPT diagram and [\ion{S}{2}]/H$\alpha$) combined with the morphology are more consistent with AGN or LI(N)ER-like ionization than with pure warm ionized medium or \ion{H}{2} region-like photoionization. Separately, we offer compelling reasons to argue that PG\,0931+691 cannot be the source of ionizing power for WPS\,46. We suggest that WPS\,46 is associated with an intermediate velocity complex (IVC) and that H$\alpha$ and nebula emission may arise as a result of a shock. We conclude by outlining a plan of action of using SDSS's Local Volume Mapper along with deep narrow band imagery obtained by amateur astronomers to explore and study the ionized sky on sub-degree scales, in general, and specifically studies of IVC and high-velocity complexes.
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All authors S. R. Kulkarni, Zeren Lin, Charles Beichman, Alex S. Hill, Xihan Deng, Tryston Raecke, Mateusz Matuszewski, Drew M. Miles, Marty Anderson, D. Christopher Martin
Astrophysics of Galaxies
The complex kinematics of the young stars orbiting the supermassive black hole in the Galactic center can be explained by the presence of an intermediate mass companion of Sgr A$^\star$
Xiaochen Zheng, Long Wang, Douglas N. C. Lin et al. (+2 more)
The sub-parsec proximity around the Sgr A$^\star$ supermassive black hole (SMBH) in the center of the Milky Way contains an inner cluster of eccentric S-
stars with randomly oriented orbits, a midway-disk of clockwise-rotating
stars (CWSs), and a surrounding population of off-the-disk
stars (ODSs). Despite their diverse kinematic properties, all three-populations appear to be massive (WR/O/B types) and have similarly limited life span $\tau_\star \sim 6-15$ Myr. Several scenarios, including
star formation induced by SMBH's close encounters with one or more gas clouds as well as impulsive close scattering by a putative intermediate-mass companion (IMC) of Sgr A$^\star$ possible an intermediate-mass black hole (IMBH), have been proposed to explain piecemeal for the origin and dynamical
evolution of S-
stars, CWSs, ODSs, as well as hyper-velocity
stars in the
Galaxy. But, their coexistence and the origin of a recently discovered zone of avoidance in S-
stars' eccentricity-peri-centric-distance distribution remain enigmatic. Here, we construct a unified model to comprehensively take into account these
stars' interaction with each other, their single natal disk, and an independent IMC. We show their disparate present-day orbits would only be concurrently attainable, within their multi-Myr age, under the combined influence of IMC's secular perturbation and these
stars' resonant relaxation in a depleting gaseous-disk environment.
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All authors Xiaochen Zheng, Long Wang, Douglas N. C. Lin, Andreas Burkert, Shude Mao
High Energy Astrophysical Phenomena
Precise scaling relations for self-interacting bosonic dark matter stars
Zhaorui Zhang, Xudong Wang and Bin Qi
The structural properties of bosonic dark matter
stars are systematically investigated, presenting precise scaling relations for the mass, radius, central density, and the properties of dark matter particles. The dark matter equation of state is derived from a complex scalar field theory with a quartic self-interaction potential $V(\phi) = \frac{\lambda}{4} |\phi|^4$, considering
boson masses $m_{\phi}$ ranging from $10^{-9}$ to $10^{3}$ GeV and self-coupling constants $\lambda$ ranging from $0.01\pi$ to $100\pi$. The scaling relation for the maximum mass of bosonic dark matter
stars, the corresponding critical radius and critical central density are obtained as \[ M_{\text{max}} = 0.1 \frac{\sqrt{\lambda}}{m_\phi^2} M_\odot, \qquad R(M_{\text{max}}) = 0.9 \frac{\sqrt{\lambda}}{m_\phi^2} \ \text{km}, \qquad \varepsilon_{\text{max}} = 2.1 \times 10^5 \frac{m_\phi^4}{\lambda} \ \mathrm{MeV/fm^3}, \] where $m_\phi$ is in GeV, the relations for $R(M_{\text{max}})$ and $\varepsilon_{\text{max}}$ are first put forward. The fitting relative error is less than $4\%$. Based on these scaling relations, we further provide global analytical fits for the stable branch. The relationships between mass and central density as well as radius and central density can be described by a unified function of the form: \[ \tilde{Y} = \frac{A}{\left[1 + \left(5\tilde{\varepsilon}\right)^h\right]^s}, \] where for $Y=M$, $\tilde{M} \equiv M/M_{\text{max}}$, $A=1$, $h=-2$, $s=0.42$; for $Y=R$, $\tilde{R} \equiv R/R(M_{\text{max}})$, $A=1.634$, $h=1$, $s=0.28$; and $\tilde{\varepsilon} \equiv \varepsilon_0/\varepsilon_{\text{max}}$. The fitting relative error is less than $0.1\%$. Furthermore, we find a simple quadratic
polynomial mass-radius relation for bosonic dark matter
stars.
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Astrophysics of Galaxies
Rapid intermediate-mass black hole formation via runaway mergers of black holes
Yining Sun and Long Wang
Observations indicate that supermassive black holes (SMBHs) in high-
redshift galaxies formed on timescales far shorter than classical growth models allow. One hypothesis suggests intermediate-mass black hole (IMBH) seeds as an efficient growth channel. Using N-body simulations, we demonstrate that in dense
stellar-mass black hole (BH) clusters ($\ge 5\times10^9 M_{\odot}/{\rm pc}^3$), runaway gravitational-wave binary BH (BBH) mergers can produce a $\sim 10^3 M_\odot$ IMBH within 10 Myr from the formation of the BH subsystem. This scenario is simple and avoids large uncertainties regarding
stellar mergers and
evolution in the IMBH formation via very massive
stars channel. We find that the runaway GW-merger mechanism relies on hard BBH formation through a chain of exchanged soft BBHs with accumulated hardening, which is far more efficient than three-body scattering. We analyze how IMBH formation depends on cluster density, total mass, initial mass function, and
stellar halo potential. We find that due to cluster expansion, the systems forming IMBHs have densities consistent with present-day
nuclear star clusters, such as those in the Milky Way and M33. Furthermore, we show that IMBH
spin remains low due to repeated mergers, and we estimate the rate of GW190521 and GW231123-like events within the first 100 Myr to be $2.27-247.52$ and $3.23-63.63 $ per Gyr per cluster.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det
A Polarization-Decomposed Method for Simulating Inhomogeneous Birefringence in Laser-Interferometric Gravitational-Wave Detectors
Haoyu Wang, Yuta Michimura, Keiko Kokeyama et al. (+9 more)
Birefringence in test mass substrates is an emerging limitation for current and future
laser-interferometric gravitational-wave detectors, particularly as detectors move toward higher circulating power, cryogenic operation, and crystalline optical materials. Spatially varying birefringence alters both the polarization state and spatial mode content of the intracavity field, reducing interference contrast and coupling into length and
alignment control signals. Accurate modeling of these effects is complicated by the fact that most frequency-domain simulation tools employ scalar modal propagation and lack native support for polarization and two-dimensional substrate maps. In this work, we present a practical and general method for simulating inhomogeneous birefringence without modifying existing simulation frameworks. The approach represents the two polarization components as independent scalar fields and introduces their coupling through an equivalent triple-Mach-Zehnder construction that reproduces the Jones
matrix of a birefringent medium. We demonstrate the method using realistic birefringence maps of the KAGRA sapphire input test masses. The technique is compatible with any frequency-domain interferometer model and enables efficient birefringence studies for next-generation gravitational-wave detectors.
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All authors Haoyu Wang, Yuta Michimura, Keiko Kokeyama, Daniel Brown, Yoichi Aso, Marc Eisenmann, Matteo Leonardi, Yutaro Enomoto, Takafumi Ushiba, Hiroaki Yamamoto, Masaki Ando, Kentaro Somiya
High Energy Astrophysical Phenomena
Discovery of CO Clouds Associated with the X-ray Jets of SS 433: Evidence for Shock-Cloud Interaction Enhancing Nonthermal X-ray Emission
Haruka Sakemi, Hidetoshi Sano, Yasuo Fukui et al. (+7 more)
We report the first identification of molecular clumps directly associated with the re-brightening regions of the large-scale X-ray jets of SS 433, based on $^{12}$CO ($J$ = 1–0) observations with the Nobeyama 45-m
Radio Telescope. Multiple clumps are detected toward the eastern and western jet heads, showing clear spatial correlation with the X-ray emission. The X-ray emission peaks immediately downstream of the molecular clumps, while the hardness ratio is enhanced at their surfaces, indicating that the observed structures cannot be explained by absorption effects. These results provide direct evidence for shock–cloud interactions between the jets and the surrounding interstellar medium. We suggest that
turbulence generated at the jet–cloud interface amplifies
magnetic fields, producing the observed non-thermal X-ray emission. Our findings highlight the importance of jet–ISM interactions in shaping the X-ray properties of microquasar jets.
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All authors Haruka Sakemi, Hidetoshi Sano, Yasuo Fukui, Mami Machida, Shigeo S. Kimura, Masato I.N. Kobayashi, Kazuho Kayama, Hiroaki Yamamoto, Kengo Tachihara, Hiroshi Nagai
High Energy Astrophysical Phenomena
Relativistic Thermal Emission from Accretion Disks in Kerr-MOG Spacetimes
Cheng Liu, Xu-fan Hu, Yosuke Mizuno et al. (+1 more)
In Scalar-Tensor-Vector
Gravity (STVG, also known as MOG), a massive vector field $\phi_\mu$ generates a repulsive fifth force that endows rotating black holes with a gravitational charge $Q \propto \sqrt{\alpha}\,M$, modifying the near-horizon geometry through a single deformation parameter $\alpha$. We investigate how this vector-field coupling imprints itself on the thermal continuum emission of geometrically thin, optically thick
accretion disks in the Kerr-MOG black hole. By re-deriving the innermost stable circular orbit (ISCO), the Novikov-Thorne radiative flux, the relativistic energy shift, and the null geodesic structure for the Kerr-MOG spacetime, we compute fully relativistic disk spectra across a broad range of
spins, inclinations, and fifth-force strengths using a dedicated xspec spectral model (kmspec). We find that the fifth-force charge pushes the ISCO outward, lowers the peak disk temperature, and systematically softens the thermal continuum relative to its Kerr black hole counterpart at the same
spin, with the deviation amplified at high observer inclinations. The resulting spectral modification closely mimics a reduction of
spin in the pure Kerr black hole framework, indicating that independent
spin measurements from, e.g., iron-line reflection spectroscopy are indispensable for disentangling the vector-field contribution. All results recover the standard Kerr black hole predictions when $\alpha = 0$, and the model is validated against independent analytic and numerical
benchmarks to machine precision. Application to a 69.6~ks XMM-Newton observation of LMC~X-1 yields $\alpha < 0.044$ at 90% confidence, consistent with the Kerr metric and general relativity.
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All authors Cheng Liu, Xu-fan Hu, Yosuke Mizuno, Tao Zhu
Cosmology and Nongalactic Astrophysics
Mock Catalogs of Strongly Lensed Gravitational Waves via a Halo Model Approach with Space-borne Detectors
Mingqi Sun, Kai Liao, Youkai Li et al. (+6 more)
Future space-borne gravitational-wave (GW) detectors, such as LISA and DECIGO, are expected to detect a large number of GW events, a fraction of which may be strongly lensed by intervening
galaxies or
galaxy clusters. In this work, we develop a comprehensive framework to simulate strongly lensed GWs in the context of space-borne detectors. Based on realistic astrophysical models for both the source population and the lens distribution, we construct mock catalogs of lensed GW events, referred to as GW-LMC-Space. Our results show that, for a four-year LISA observation, the expected number of lensed events ranges from $0$ to $131$, depending on the adopted formation model of massive black hole binaries (MBHBs). The corresponding
lensing probability for MBHBs can reach up to $\sim 0.3\%$. For DECIGO, we find that the number of lensed events in a one-year observation is expected to lie in the range of $0$–$44$, with a
lensing probability of $\sim 0.15\%$ for
stellar-mass binary black holes (BBHs), binary
neutron stars (BNSs), and
neutron star–black hole binaries (NSBHs). We further show that the overlap of lensed signals is a common feature in space-borne detectors, which can significantly affect both the signal-to-noise ratio (SNR) estimation and event identification. These results highlight the importance of accounting for signal overlap in the analysis of strongly lensed GW events in future space-borne GW observations.
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All authors Mingqi Sun, Kai Liao, Youkai Li, Tonghua Liu, Hengyu Wu, Shaoqi Hou, Tao Yang, Xilong Fan, Marek Biesiada